We study the phenomenon of strategic group polarization in which members take more extreme actions than their preferences. The analysis is relevant for a broad range of formal and informal group settings, including social media, online platforms, sales teams, corporate and academic committees, and political action committees. In our model, agents with private preferences choose a public action (voice opinions), and the mean of their actions represents the group’s realized outcome. They face a trade-off between influencing the group decision and truth-telling. In a simultaneous move game, agents strategically shade their actions towards the extreme. The strategic group influence motive can create substantial polarization in actions and group decisions even when the preferences are relatively moderate. Compared to a simultaneous game, a randomized sequential actions game lowers polarization when agents’ preferences are relatively similar. Sequential actions can even lead to moderation if the later agents have moderate preferences. Endogenizing the order of moves (through a first-price sealed-bid auction) always increases polarization, but it is also welfare enhancing. Our findings can help group leaders, firms, and platforms design mechanisms that moderate polarization, e.g., the choice of speaking order, the group size, and the knowledge members have of others’ preferences and actions.